This invention relates to an ultrasonic transducer probe having a mechanically steered acoustic element so that the ultrasonic beam can be steered within a sector of a plane. The probe is primarily intended to be used for ultrasonic imaging of biological tissue structures together with blood velocity measurements and imaging of blood flow.
There exist in the market several similar devices for similar applications. The problem with present devices is that it is difficult to do simultaneous imaging and Doppler measurements. Using the Missing Signal Estimator method, as described in U.S. patent application Ser. No. 440,255 filed Nov. 9, 1982, it is possible to obtain for practical purposes simultaneous 2-Dimensional (2D) amplitude imaging and Doppler blood velocity measurements along a defined beam direction, if the transducer can be stopped very quickly from its sweeping motion during imaging to do the Doppler measurement along the defined beam direction, and then be rapidly accelerated after the measurement to perform a new imaging sweep. The present invention provides a design for achieving rapid acceleration of beam direction movement so that for practical purposes simultaneous imaging and Doppler measurement can be attained. The rapid acceleration achieved is also useful for combined 2D tissue imaging and 2D flow measurements, as described in U.S. patent application Ser. No. 603,511 filed April 24, 1984.
At this point reference is made to U.S. Pat. No. 4,421,118 (Dow) in which an ultrasonic transducer is disclosed. The Dow transducer comprises a transducer head assembly containing a movable holder having a transducer element coupled to a stationary base by a mechanical linkage. A motor adapted to provide linear reciprocating motion is coupled to the mechanical linkage for causing the element holder and element, when driven by the motor, to undergo reciprocating swinging motion for transmitting ultrasonic energy to and receiving echo signals from an object in front of the transducer in a sector scanning manner. The mechanical linkage in this known arrangement, however, has serious drawbacks which are particularly related to the problem of obtaining a rapid acceleration of the angular sweep.
Thus the novelty of the present invention lies in the mechanical design by which rapid acceleration of the beam direction can be achieved so that complex sweep sequences can be obtained as, for example, that illustrated in FIG. 1 and further described hereinafter.
A Missing Signal Estimator, in accordance with U.S. patent application Ser. No. 440,255 of Nov. 9, 1982, is used to generate a Doppler substitute signal based on Doppler measurements in the intervals when the transducer stands still. This Doppler substitute signal is utilized in the periods during which 2D tissue or flow imaging is performed, so that an apparently simultaneous imaging and Doppler measurement is obtained.
The purpose of the present invention of an ultrasonic probe design is accordingly to obtain a rapid acceleration of the transducer so that the periods of switching the beam direction can be kept sufficiently small as to be practically negligible, with tolerable vibration of and power consumption by the transducer. It is also important, especially for flow imaging, that the beam motion be smooth in the sweep intervals so as to avoid high Doppler shifts from tissue.
According to the present invention the foregoing are attained in an ultrasonic transducer probe having a mechanically steerable acoustic element which includes a linear motor having a stationary magnet assembly and a coil bidirectionally linearly movable with respect to the magnet assembly. A mechanical arrangement formed of a pair of spaced apart, rotatably mounted pulleys and a flexible belt connecting the pulleys couples the coil and an ultrasonic transducer or acoustic element. The transducer element is mounted for rotation with at least one of the pulleys so that linear motion of the motor coil is converted to rotative motion of the transducer whereby the transducer and the ultrasonic beam it emits is caused to sweep through a selected angular sector. A position sensor formed of a supplemental stationary magnetic material and a position coil mounted for movement with the motor coil is utilized for detecting the linear position of the coil and, correspondingly, the angular orientation or position of the transducer element.
Further objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of a presently preferred, but nonetheless illustrative, embodiment in accordance with the present invention when taken in conjunction with the accompanying drawing.